Bifröst

To reach those dwellings the gods made a bridge from earth to heaven, which people call the rainbow. Gylfaginning says it has three hues and was made with more art than any other work, and that the gods ride over it every day to hold court at the Urðr fount. Thor alone goes on foot and wades the rivers, or the bridge would be in flames. Strong as it is, it will break when the sons of Muspell ride over it.